Notorious Jeep tick...

[Wrench]

So,
I had a ticking that suddenly started in my Cherokee engine several months back. All indications pointed toward the valve-train, and I was beginning to think I had a lifter go flat.

2 weeks ago I decided to pull the valve cover and take a look. Turns out, one of the valve spring retainer keepers was starting to let go of the valve. This allowed the retainer to creep up and start contacting the rocker arm slightly, which was causing the ticking noise.

I had also noticed the engine cutting out at a lower RPM than when I first rebuilt the engine; a good indication of valve float. I am thinking the keeper problem is a side-effect of the valve float. I guess the stock valve springs, even with the stock cam, are not too happy over 6k rpm.

I ordered a set of hardened keepers and stiffer valve springs from Summit and installed them. She seems to be much happier now!

Keepers: pn HRS-93020
Springs: pn CCA-901-16

The springs were a little larger diameter than the stock springs, but fit well with a little trimming. These would probably be good on the 4.0 head also, since they have the same dimensions as the 2.5 head.

[OldGreen]

They also work on 258s and AMC V8s.

I have a few of them around the house. . .

[Roman]

Wrench, how do these springs specs compare to stock? How much stronger are they?

Comp Cams Spring Rate 353 lbs./in.
Stock AMC 2.5 Spring Rate ??? lbs./in.

Will seat pressure be too high for stock head/lifters?

[Wrench]

Wrench, how do these springs specs compare to stock? How much stronger are they?

Comp Cams Spring Rate 353 lbs./in.
Stock AMC 2.5 Spring Rate ??? lbs./in.

Will seat pressure be too high for stock head/lifters?

These springs are 353 lbs/in spring rate with a seat pressure of 101 lbs at stock 1.65" installed height.

The stock springs are supposed to be around 65 lbs of seat pressure at installed height with a rate of 295 lbs/in.

Ideally, if one was to want to run a really hot cam with lots of lift, you can use the Chevy retainers (for less weight, and smaller diameter for valve cover clearance) with the keepers I listed above, and use a good set of beehive style springs. You would have to cut the spring seats in the head, though, since most of the springs run between 1.8"-2.0" of installed height. The beehive springs and smaller Chevy retainers would allow for less chance of valve float with a lighter seat pressure/spring rate and less stress on the 5/16" rocker bolts than a standard style spring. The rockers/bolts seem to be the limit to these heads, as many have had problems trying to install 3/8" studs.

Then again, there really isnt much for cam selection for the 2.5, so this info is really more pertinent to the 4.0 crowd.

[Roman]

the 2.5 and 4.0 are pretty much the same valve train?

[Wrench]

the 2.5 and 4.0 are pretty much the same valve train?

Yep.

Valves are also identical, up to a point. Somewhere in the mid 1990's, the 4.0 switched from valve stem locks with one groove (like the 2.5) to locks with several grooves.

The engines are the same bore and stroke also. I believe the 4.0 pistons are directly interchangeable with the 2.5.